This invention relates to the art of accelerometers and more particularly to fiber optic accelerometers.
Heretofore, various types of accelerometers have been used. In one type of accelerometer, a mass is displaced against a spring by the inertial force due to acceleration. The distance which the mass is displaced varies with the acceleration. By monitoring the amount of displacement, the acceleration can be determined. The smaller the acceleration which the prior art acceleration accelerometers are designed to measure, the more sensitive they tend to be to interference. Further, the accuracy of accelerometers is related to the linearity or predictability of the physical changes in response to acceleration. Commonly, it is difficult to maintain the linearity and predictability when measuring relatively small accelerations.
In one prior art fiber optic accelerometer, a mass is positioned in a housing by transverse diaphragms. The mass is suspended between the ends of longitudinally extending tensioned optical fibers. The tensioned optical fibers are secured to the mass and the housing such that under acceleration, the mass elongates one of the fibers and allows the other to contact. Each fiber is mirrored at the end connected to the mass. A laser transmits phase coherent light along both optical fibers toward the mirrored ends. Light reflected from the mirrors is combined and fed to a signal processor or other phase shift detector. The elongation and contraction of the optical fibers caused by acceleration alters the phase relationship of the two reflected light beams. The detected phase shift varies in accordance with the acceleration.
The present accelerometer contemplates a new and improved accelerometer which is capable of measuring small acceleration forces accurately over a wide dynamic range. For example, in the preferred embodiment, the accelerometer is able to measure accelerations on the order of one-millionth the acceleration of gravity.